Process for the preparation of a raw material suitable for iron production

ABSTRACT

A process for manufacturing a raw material suitable for iron production, from a precipitate derived from the electrolytic zinc process and mainly containing alkaline sulfates of iron, such as glockerite Fe4SO4(OH)10, ferrihydroxosulfate FeSO4OH, or jarosite A(Fe3(SO4)2(OH)6), in which A is an alkali metal, NH4, or H3O, and hydroxides, such as goethite FeOOH and ferrite (mainly zinc ferrite ZnFe2O4), and for recovering the valuable metals, such as zinc, copper, cadmium, etc., present in the precipitate, is disclosed in which a precipitate slurried in water or a mild sulfuric acid solution is treated hydrothermally at an elevated temperature so that the operation remains within the stability range of haematite Fe2O3 in the system Fe2O3-SO3-H2O, whereafter the haematite-containing solid suitable for iron production is separated from the solution containing valuable metals.

United States Patent [191' [111 3,910,784 Rastas Oct. 7, 1975 PROCESS FOR THE PREPARATION OF A RAW MATERIAL SUITABLE FOR IRON PRODUCTION Appl. N0.: 437,5 l8

[30] Foreign Application Priority Data Feb. 1, 1973 Finland A. 294/73 [52] U.S. Cl. 75/1; 75/101; 75/120; 75/121 [51] Int. Cl. C22B 1/00 [58] Field of Search 75/1, 97, 21, 23,101, 75/120, 121

[56] References Cited UNITED STATES PATENTS 3,434,947 3/1969 Steintveit 75/l2l 3,493,365 2/1970 Pickering 75/120 3,676,]07 7/l972 Barnard 75/121 Primary Examiner-Peter D. Rosenberg Attorney, Agent, or FirmBrooks Haidt Haffner & Delahunty [57] ABSTRACT A process for manufacturing a raw material suitable for'iron production, from a precipitate derived from the electrolytic zinc process and mainly containing alkaline sulfates of iron, such as glockerite Fe SO (OHM), ferrihydroxosulfate FeSO OH, or jarosite A[- Fe (SO (OI-I)6], in which A is an alkali metal, NH or H 0, and hydroxides, such as goethite FeOOl-l and ferrite (mainly zinc ferrite ZnFe O and for recovering the valuable metals, such as zinc, copper, cadmium, etc., present in the precipitate, is disclosed in which a precipitate slurried in water or a mild sulfuric acid solution is treated hydrothermally at an elevated temperature so that the operation remains within the stability range of haematite Fe O in the system Fe O SO H O, whereafter the haematitecontaining solid suitable for iron production is separated from the solution containing valuable metals.

13 Claims, 2 Drawing Figures US. Patent Oct. 7,1975

Fe SO4(OH) 140C glkg H2504 glkg 200C 40- F P so OH I l I l l 10 20 40 80100 200 Sheet l l I l l I l I I I 10 2O 40 100 F8 50 (CH) Fig. 2

H 50 glkg System Fe O -SO -H O at temperature range 140-200 C according to articles Posnjak & Merwin (on the left) and Walter Levy & Qumneur (on the right) (cf. specification PROCESS FOR THE PREPARATION OF A RAW MATERIAL SUITABLE FOR IRON PRODUCTION BACKGROUND OF THE INVENTION The present invention relates to a process for producing, from a precipitate from an electrolytic zinc process, a raw material suitable for iron production.

A sulfidic concentrate, which is the raw material used in a conventional electrolytic zinc process, normally contains, in addition to zinc sulfide, which is its principal component, Fe 3-12 percent, Pb and SiO each about 1 percent, and Cu, Cd, Mn, Mg, Ca, Ba, Al a few tenths of a percent. The concentrate also contains small amounts of silver (-100 ppm) and gold 1 p In addition to the main reaction, the oxidation sulfides, some ferrite formation also takes place in the oxidating roasting of a sulfidic concentrate:

MeO Fe O MeFe O (1 This ferrite formation is of great importance in the further treatment of the roasted product. Reaction (1) is almost complete under the roasting conditions so that practically all the iron present in the roasted product is in a ferrite form, the main product being Zinc ferrite ZnFe O Until recently, the roasted product has been leached in a mild sulfuric acid solution so that the oxides dissolve and the bulk of the ferrites remain undissolved. The reason for this has been the difficulty of precipitating, in a well filtratable form, the great iron amounts produced when leaching ferrites. The leach residue produced as a result of such a leaching treatment thus mainly consists of ferrites, but it also contains insoluble sulfates and other insoluble compounds such as silicates.

With iron contents of 3-12 percent in the zinc concentrate, the leach residue contains 3-12 percent of the total zinc fed into the process. The percentages of copper and cadmium in the leach residue are considerably higher than that of zinc.

Both pyroand hydrometallurgical processes have been developed for the further treatment of this primary leach residue and for the recovery of the valuable materials present in it; such processes are described in, for example, Finnish Patent Application 508/71.

ln hydrometallurgical processes the ferrite-containing leach residue has been leached in the zinc electrolysis return electrolyte. The solid remaining after this leaching and containing the undissolved ferrites, poorly soluble sulfates (PbSO CaSO BaSO most of the silicon (in the form of SiO and the silver and the gold has usually been separated from the solution and fed into processes in which it has been possible to separate and recover the valuable materials (Pb, Ag, Au) present in it. The solution, the iron (Fe(lll)) and sulfuric acid contents of which usually vary within 20-35 g/l, has been fed directly or after a preneutralization into the iron precipitation stage. The ferric iron has been precipitated as alkaline sulfate and/or oxohydroxide. A roasted zinc product has usually been used for neutralizing the sulfuric acid released in the precipitation reactions. The ferrite part of the roasted product does not dissolve during the precipitation stage but remains in the iron precipitate. ln some processes, salts of sodium or ammonium have also been fed into the iron precipitation process, in which case the iron precipicorresponding to some 2-6 percent of the total zinc feed of the process, remains after the process. Although the relatively high rate of zinc carried away in the iron precipitate can be considered a disadvantage, the main disadvantage of these processes consists of the high iron precipitate rates (the zinc production being 3-12 percent, about 20,00080,000 t/yr of iron precipitate) in most cases this precipitate must be considered as waste.

The acid wash of ferrite-containing jarosite precipitate has been developed for a partial recovery of the zinc present in the iron precipitate. A considerable part of the ferrites of the precipitate can be brought into a solution by an acid wash.

The leach residue of a conventional process and the ferrite-containing iron precipitates mentioned above have also been treated with a combination of chlorinating and sulfating roasting (A. Roeder, H. Junghans, H. Kudelka, Process for Complete Utilization of Zinc Leach Residues, Journal of Metals 21 (1969) 31-37). The product of this treatment is an iron oxide ore with such a low non-iron content that it can be used as such Moriyama, Y. Yamamoto, Akita Electrolytic Zinc.

Plant and Residue Treatment of Mitsubishi Metal Mining Company Ltd. Proceeding of AlME-World Symposium on Mining and Metallurgy of Lead and Zinc (1970) Vol. 2). In this process, the product obtained after the water leaching of a sulfated roasted product is an iron oxide precipitate the zinc content of which is still so high that it cannot be used as raw material in iron production,

All the above processes have a disadvantage either in a deficient recovery of zinc and high iron precipitate rates mostly remaining as waste or in that it has not been possible to link the iron precipitate treatment process directly to an electrolytic zinc process. It must be especially underlined that even though high rates of recovery of zinc, copper and cadmium are obtained in hydrometallurgical processes in which the iron is precipitated in the form of jarosite and an acid wash of the jarosite precipitate has been linked to the process, the waste problem caused by high iron precipitate rates remains unsolved. lt can be expected that in the future this waste problem will be accentuated and it is necessary to find a satisfactory solution.

U.S. Pat. No. l 834 960 discusses a case in a roasted zinc product, the ferrites of which had been left in the iron precipitate in accordance with the cases described above, was used for the neutralization. Thereafter, the iron precipitate was roasted in a Wedge furnace within the temperature range 500-600C. In

which the iron was precipitated as an alkaline sulfate. In this case,

3 this treatment, the alkaline sulfates decomposed and part of the zinc of the zinc ferrite ended up in a watersoluble sulfate. After a water wash, the zinc content of the roasted product was about percent, of which 50-60 percent was in a water-insoluble ferrite form.

In the roasting process described above, as well as in the sulfating roasting of the primary leach residue described earlier, the sufficiently complete sulfating of the zinc ferrites remains an unsolved problem. After a water wash of the roasted product, the zinc content of the iron oxide precipitate, i.e., the zinc in ferrite form, remained in both cases at 2-3 percent, in which case the iron oxide precipitates were not directly applicable to iron production.

The above disadvantages have been eliminated in a process in which an alkaline precipitate, mainly containing alkaline sulfates and hydroxide of iron, and zinc ferrite, is treated thermally so that the partial pressures of oxygen and sulfur in the system ZnFeS-O and the temperature are controlled within the thermal stability range of ZnSO Fe O in which case the zinc and certain other non-iron metals are converted into water-soluble sulfates, and the iron present in the alkaline sulfates, hydroxide, and ferrite of the precipitate is converted into an oxidic form. The product obtained by the thermal treatment is leached. The solution is separated from the undissolved iron oxide precipitate and returned to the leaching circuit of the roasted zinc product. A well washed iron oxide precipitate can be fed into iron production. To bring the zinccontent of the washed iron oxide precipitate to 0.1-0.2 percent prerequires a rather complete sulfating of the zinc ferrite on the one hand, and a precise control of the circumstances on the other hand, so that the recompounding of zinc ferrite can be prevented as completely as possible. A precise control of the S0 and O rates in the gas phase and the appropriate temperature corresponding to them can be best obtained in a fluidizedbed reactor.

Even though an almost complete recovery of zinc, copper, and cadmium can be achieved by this process and in most cases the waste problem caused by the iron precipitate can be solved advantageously, the process leads to the treatment of relatively large amounts of gas and thereby to rather expensive solutions in terms of equipment. In addition, a filter-dry material (humidity 25-35 percent) must first be dried and then the product obtained from the thermal treatment must again be mixed with water into a slurry.

SUMMARY OF THE INVENTION According to the invention a precipitate derived from the electrolytic zinc process is slurried in water or a mild sulfuric acid solution, then the slurry is treated hydrothermally at an elevated temperature under conditions wherein haematite is stabile in the system Fe O SO I-I O and finally the raw material is separated from the metal value containing solution.

The present invention is specifically based on the principle that the conversion, into an oxidic, zinc-poor form, of the alkaline sulfates and zinc ferrites produced in electrolytic zinc processes is carried out hydrothermally, in which case, when suitable roasted zinc products are used for the precipitation of the iron, the precipitate which has undergone the hydrothermal conversion is directly usable as raw material in iron production in which case the waste problem caused by large iron precipitate amounts in connection with an 4 electrolytic Zinc process is solved, and the iron previ ously bound to waste can be channeled to useful purposes. This hydrothermal conversion can be carried out in an autoclave, preferably within the temperature range l50-280C. The thickened or filtered and water-slurried solid material emerging from the iron precipitation of the zinc process or from the acid wash of this precipitate is fed into an autoclave, which is preferably of the tubular type. The temperature in the autoclave is controlled within l50-280C. When a suitable and sufficiently high temperature is chosen considering the composition of the precipitate, the delay period of the solid material at the maximum temperature can be reduced to some tens of minutes, in which case the space requirement of the autoclave treatment is relatively small especially when considering that the solid material content of the slurry in the autoclave can be quite high, e.g., 300-800 g/l. As can be seen from reactions l l and l2), sulfuric acid, which is consumed in the leaching of the zinc ferrites (reaction 13)), is produced at the conversion stage. It is very typical of the process that the sulfuric acid contents of the solution remain moderate and that the conversion is possible even with quite a high solid content and can take place within a relatively short reaction period. In this case it is possible to solve corrosion problems advantageously, and small autoclave volumes are sufficient; the autoclave can well be of the tubular type, for example.

Owing to all these factors the process can be achieved with moderate equipment costs, which is especially important in this case because the valuable content of the solid material to be treated is low, and the point is mainly to solve the waste problem caused by an iron precipitate with a great volume but a low valuable content. These treatment and equipment costs are considerably less than if the precipitate were treated purely thermally from a sulfate form to an oxidic form. Also, the treatment in the process according to the present invention is considerably simpler and more economic than when combining as is done in some processes the leaching of ferrites and the precipitation of iron in an autoclave in one treatment stage (A. S. Yarolavtsev, V. I. Smirnov, Tests on the Autoclave Leaching of Zinc Cakes, Tsvetney Metally 6 (5) (1965) 31) or when the aim is to precipitate the ferric iron by an autoclave treatment of the solution immediately after the leaching of ferrites.

In these processes the solution and slurry amounts to be treated are considerably larger (3-7-fold) since in them the treatment takes place in the main flow of the process. In addition, when the iron is precipitated by an autoclave treatment from a ferrisulfate-containing solution and the aim is to obtain an iron precipitate which contains as much haematite as possible, the sulfuric acid contents involved are high (reaction (14)) and then it is not possible to obtain iron precipitates containing mainly haematite, because in this case it is often necessary to operate within the stability range of the solid phase FeSO OH (cf. Annex 2). The high sulfuric acid contents especially when large solution amounts must be treated cause considerable expenses in terms of equipment.

In the process according to the present invention, the solid is separated from the solution after the hydrothermal treatment and washed well in water. The solution is returned to the leaching circuit of the electrolytic zinc process and the washed precipitate can be fed as raw material into iron production.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows some phase diagrams of the system Fe O SO H O at the temperature interval 75l25C and FIG. 2 at the temperature interval l40200C.

. DESCRIPTION OF THE PREFERRED EMBODIMENTS Before describing the process according to the present invention in detail it is appropriate to discuss certain general laws pertaining to the system Fe O SO- H O; the process according to the present invention is also based on them.

FIGS. 1 and 2 show the stability graphs of the system Fe O -SO H O drawn on the basis of the following articles: E. Posnjak, H. E. Merwin, J. Amer. Chem. Soc. 44 (1922) 1965, L. Walter-Levy, E. Quemeneur, C. R. Acad. Sc., Paris, 258 (1964) 3028, L. Walter- Levy, E. Quemeneur, Bull Soc. Chim., France 6 (1966) 1947.

In the system discussed, the hydrolysis reaction taking place at various temperatures can be generally presented as follows:

Fe O xSO -yl-I O(s) (3 x)H SO (aq) or in the corresponding ionic form 2Fe (aq) xSO (aq) (3 x y)H Of-= Fe O xSO -yH O(s) 2(3 x)H (aq) (3 The following solid material phases Fe O 'xSO 'yH O appear within this interesting concentration and temperature range:

Table 1 6 NH (of these, only sodium and ammonium .have any practical importance in connection with the zinc process). When the solution contains the component A 80 (e.g., Na SO or (NH SO at the rate of even a few grams a liter, almost solely the following reaction (4) takes place in the place of reaction (3):

3Fe (aq) 2SO (aq) xA (aq) (7 x)H O 1-( a )1-.r[ 3( 4)2( )6](- x)l-I (aq) The iron then precipitates as a jarosite-type mixed crystal A (H O), [Fe (SO.,) (OH) The compounds A[- Fe (SO.,) (OH) (A alkali, NH.,) and H O[Fe SO (OH) (hydronium jarosite or carphosiderite) are isomorphic and form the above-mentioned mixed crystal.

If now zinc oxide or roasted zinc product is added to a solution which contains ferric iron and sulfuric acid each about 20-35 g/l neutralization of sulfuric acid takes place first until almost the total sulfuric acid has been neutralized. When the addition of the neutralizing agent is continued guided by the pH value predetermined in each case the iron begins to precipitate according to reactions (57 )'and the sulfuric acid released in the reactions begins to be neutralized by reaction (8).

3Fe (SO (aq) l4H O= a 3( 4)2( )s]( 2 4( q) 3Fe (SO (aq) ISH O 3/2Fe SO (OH), (s) 2 4( q) 3Fe (SO (aq) 125 0: 6FeOOH(s) 9H SO q) 7) ZnO(s) H SO.,(aq) ZnSO.,(aq) H 0 (8) Stable solid phases appearing in system Fe O SO H O within temperature range 75-200C and with iron (ferric) and sulfuric acid contents of I00 g/l x y solid phase second form of Fe O .xH O.yH O expression name 0 0 Fe O Fe O haematite 0 l Fe- ,O H O FeOOH goethite l/2 5/2 Fe O l/2SO ,5/2H O Fe SO,,(OH) glockerite 4/3 3 Fe 0 .4/3SO ,3H O H O[Fe,-,(SO (OH) I hydronium jarosite 2 l Fe O .2SO -,.H O FeSO ,OH ferrihydroxosulfate If the component ZnO is added to the basic system Fe O -SO;,H O' (the system then comprises solution Fe (SO ZnSO H SO H O and a solid phase which is in balance with it and the composition of which (as well as that of the solution) can be presented by using the components Fe O ZnO, S0 and H 0), component ZnO which does not participate within the here involved concentration and temperature range in any reaction in which ZnO would be part of the separated solid phase, the effect of the component ZnO on the basic system is rather insignificant. The it only affects the activities of the components Fe (SO H 0, and H 50. which participate in reaction (2), and it can thereby cause changes and displacements in the stability ranges of the solid phase Fe O 'xSO 'yH O. These changes are not, however, too great for the stability ranges given in Annexes l-2 to be utilized when evaluating, in connection with the zinc process, the different iron precipitation processes and the compositions of the solid phases obtained by them.

Nevertheless, the situation is completely different if the system mentioned above is expanded by the component A O(A SO in which A is some alkali metal or When the precipitation takes place as a batch process, the addition of the neutralizing agent being slow enough, it is possible to precipitate the iron as pure H O jarosite. In this case the pH' value is within l.l0l .30 and the temperature within -l0OC. When the addition of the neutralizing agent is accelerated in which case the pH value is respectively higher the a-FeOOH contentof the precipitate increases intensively. The pH value of the solution is then within 1.30-1.70. At the same time the filtration properties of the precipitates are abruptly worsened. The conditions prevailing in the solution at the initial stage of the iron precipitation are such that the solid phase in balance with it is H O jarosite. Even in this case, there is around the ZnO particles a diffusion layer; the stable balance phase in the conditions of this layer is glockerite or goethite. In a rapid neutralization in which case the pH of the solution is higher the goethite and glock erite precipitates formed on the surfaces of the ZnO particles will not dissolve under the average solution conditions and the final precipitate will contain these compounds. In a slower neutralization in which case the pH of the solution is lower there is a greater possibility that the formed goethite and glockerite in the form of H jarosite.

When iron is precipitated from a solution devoid of alkali and ammonium in a continuous process in a multiple-part series reactor, it is seen that the bulk of the ferric iron 70-80 percent precipitates in glockerite form and the rest 30-20 percent respectively in jarosite form. This outcome is easy to understand on the basis of the stability data given in FIG. I and the above specification of the precipitation process.

If a hydrometallurgical treatment of the primary leach residue is adopted in an electrolytic zone process, it is inevitable that at the iron precipitation stage the solutions contain small amounts of sodium ions which partly originate in the roasted product and partly in the chemicals fed into the electrolysis stage. Normally these sodium amounts are -l 5 percent of the stoichiometric sodium which would be required for precipitating, as Na jarosite, the iron carried along with the roasted product (iron content 5-10 percent). As was stated above, mixed jarosite Na,I-l O [Fe (SO (OI-D is now formed at the iron precipitation stage in addition to the compounds a-FeOOH and Fe SO (OH) and the rate of mixed jarosite grows continuously as the sodium rate grows. When the sodium rate rises to 5060 percent of the stoichiometric rate, the ferric iron is all precipitated in the form of mixed jarosite. The x value indicating the sodium proportion of mixed jarosite is then about 0.5.

Roasted zinc product is generally used at the precipitation stage of ferric iron for neutralizing the sulfuric acid released in the precipitation reactions. The ferrite part of the roasted product is then not dissolved to a noteworthy extent but remains almost completely in the iron precipitate and causes a considerable zinc ferrite content in it.

If the iron has been precipitated in a pure jarosite form, it is possible as shown in Norwegian Pat. No. 123 214 and as said earlier to selectively leach the zinc ferrite from the iron precipitate by an acid wash. If an appropriate amount of sulfuric acid or electrolysis return acid is added to the thickened jarosite precipitate slurry and the leaching conditions are kept corresponding to those of the ferrite leaching stage (temperature 90lOOC, H 50 content 30-50 g/l, solid content of the slurry 300-500 g/l, and delay period 4-10 h), the zinc ferrite dissolves while the most of the jarosite remains undissolved. If the precipitate contains glockerite and goethite, these also dissolve under the above conditions. In terms of a selective leaching of zinc ferrites, it is thus important that the precipitated iron is in jarosite form.

lf the iron has been precipitated in an atmosphere devoid of or poor in Na or NH.,, the obtained precipi tate contains glockerites, jarosites, and zinc ferrites. An acid wash is not according to the above suitable for this precipitate. To lower the zinc content of this precipitate, however, it is possible to carry out a modified acid wash of the precipitate, utilizing the stability data of the system Fe O SO H O.

Sulfuric acid equivalent to conversions (9-10) 4H O (l0) 8 is added to the thickened slurry which contains glock erite, jarosite and zinc ferrites.

It must be particularly noted in this case that the operation takes place within the stability range of H 0 ja- 5 rosite according to Annex 1, so that the thermodynamic prerequisites for the formation of H 0 jarosite do exist.

The highly ferrite-containing solution obtained as a result of this treatment is returned after the separation of the solid material to the iron precipitation stage. The high iron content at the precipitation stage favors H O jarosite formation (FIG. 1), which again reduces the dissolution of iron at the acid wash stage.

The system is driven to a stationary state where there is a certain circulating Fe load between the precipitation and the washing stage. The iron precipitate emerging from the system is not in the form of H 0 jarosite.

Nevertheless if the basic idea of this invention is put to use the conversion of an iron precipitate containing sulfate and zinc ferrite into an oxide, zinc-poor material is obtained by hydrothermal methods, i.e., by reforming the iron precipitate by an autoclave treatment, in which case the temperature suitable for, for example, a glockerite-containing precipitate is l60-200C; within this temperature range the conversion already takes place rapidly enough. A sulfuric acid addition is usually not necessary in this process. The product of the treatment is so-called purple ore or, when operating at lower temperatures, often also jarosite-containing cut zinc-poor purple ore.

The following reactions take place at the reformation Stage:

ZnSO (aq) 4H O (l3) It must be especially emphasized that under these treatment conditions the operation takes place within the range in which the stable phase is haematite or Fe O (cf. FIG. 2).

A corresponding autoclave conversion can also be used for pure jarosite precipitates instead of an acid wash or as a stage thereafter to convert a sulfateeontaining iron precipitate into an oxide-containing iron precipitate. To accelerate the jarosite haematite conversion, the operation must now take place at relatively high temperature, 220250C.

The following examples illustrate in more detail the results obtained by the process according to the invention. 55

EXAMPLE 1 In the trials, precipitates containing varying rates of zinc ferrites and varying alkaline sulfates of iron were slurried in a dilute sulfuric acid solution and closed in glass ampoules. The ampoules were immersed in oil thermostats, and put in a slow revolving motion, in which case the contents of the ampoules were subjected to a mild mixing. After a delay period of three days, the ampoules were opened and the solution and solid phases were analyzed. The aim of the trials was to obtain an approximate idea of the temperature range within which the operation should take place with each precipitate composition to achieve moderate reaction periods.

Trial '1 lnitial precipitate C Fe SO Zn Na NH, 1 2 3 4 5 Trial T Final solution "C Fe Zn H SO 1 1 :x( S04 )2(OH )4] 2 n 1 a( 4)2( )s1 3 41 -|)2( )61 4 Fe SO,(OH), ZnFe O, 6 Fe- O Trial T Final precipitate C Fe SO Zn Na NH 1 2 3 4 5 6 2 1 1 :1( 4)2( )e;1 2 H; 0[F :i( 4)-z( )n 1 3 NH,.[Fe;.(S04)z( )s1 4 Fe SO.,((')1-1) 5 ZnFe O 6 Fe- O EXAMPLE 2 was mixed with water (400 g/2 1) into a slurry into Zinc ferrite-containing jarosite precipitate taken from a technical process and with the following analysis NH 2.1 Na 0.2 Fe 31.9

which g of sulfuric acid was added. The slurry was closed in a laboratory autoclave, the temperature of which was raised to 200C. The compositions of the so- 5 lution and the solid were observed for 10 hours. Zn 6.0

Analyses Period Fe Fe Zn H Fe Zn S Na NH h g/l solid phase component distribution NH jar. Na-jar. H-jar. Zn-ferr. Fe O; E

Initial precipitate 55.9 4.4 18.3 22.2 100.8 1 h 55.9 4.4 15.2 22.0 97.5 3 h 47.9 4.0 17.0 22.9 91.8 611 8.3 0.8 4.5 3.3 71.3 88.2 0 h 0.6 12.0 0.9. 76.0 84.5

Example 3 Procedure as in Example 2, but without sulfuric acid addition. Temperature T 220C, and reaction period 6 h.

Period Fe Fe Zn H 80, Fe Zn S Na NH h g/l Example 4 Procedure as in Example 3, but T 240C.

Period Fe Fe Zn H SO, Fe Zn S Na Nl-l h g/l Example Procedure as in Example 4, but g of sulfuric acid has been added to the initial solution. Period Fe Fe Zn H SO Fe Zn S Na NH h g/l A 4.5 4.3 24.6 31.4 57.0 1.1 2.2 0.03 0.0l V2 4.1 4.0 24.0 30.7 58.5 0.34 1.8 0.03 0.0l l 5.4 5.4 25.8 30.4 58.5 0.30 1.8 0.03 0.01 2 5.4 5.2 27.1 31.9 58.6 0.26 1.7 0.03 0.0l

Example 6 Procedure as in Examples 24, but now the initial precipitate was acidwashed jarosite precipitate with the following analysis: NH 2.5%, Na 0.26%, Fe 30.6%, S 12.8%, S,= 0.18%, Zn 1.1%, SiO 4.1%. Initial amount of precipitate was 500 g, which was slurried in 1 liter of water. Temperature 280C.

Period Fe Fe Zn H 50, Fe Zn S Na SiO V4 5.4 4.6 5.3 60 55.0 0.05 2.1 0.03 6.5 k 5.5 4.9 5.5 55 55.2 0.05 2.1 0.03 6.9 l 5.5 5.1 5.5 66 55.4 0.04 2.1 0.03 7.0 2 5.5 5.2 5.5 67 55.4 0.04 2.1 0.03 7.0 4 5.5 5.2 5.5 67 55.4 0.04 2.1 0.03 7.4

What is claimed is:

l. A process for the preparation of a raw material suitable for iron production from a precipitate derived from an electrolytic zinc process and comprising basic sulfates and hydroxides of iron and zinc ferrite, and for recovering other metal values in the precipitate, comprising:

forming a slurry of the precipitate in water;

converting iron in said slurry into haematite Fe O by treating said slurry hydrothermally in an autoclave at a temperature between about 150C and about 280C while maintaining operating conditions within the stability range of haematite Fe O in the system Fe O SO -H O to form haematite containing solid material suitable for iron production and a solution containing said other metal values; and

separating said haematite containing solid material from said solution.

2. The process of claim 1, in which the precipitate is slurried in water mildly acidified with sulfuric acid.

3. The process of claim 1, wherein the precipitate contains zinc ferrite and at least one of the following basic sulfates of iron: glockerite. ferrihydroxosulfate. and jarosite A/Fe SO (Ol-l) in which A is selected from the group consisting of an alkali metal ion, NH. and H O 4. The process of claim 1, wherein the precipitate contains at least one of the following hydroxides of iron, namely goethite and a ferrite.

5. The process of claim 1 for treating a precipitate containing mainly glockerite and zinc ferrite, in which the hydrothermal treatment is carried out at a temperature of about l60l4 200C.

6. The process of claim 1 for treating zinc ferrite and a pure jarosite precipitate, in which the hydrothermal treatment is carried out at a temperature of about 220250C.

7. The process of claim 1, in which the slurry to be treated has a solid material content of about 200-800 g/l.

8. The process of claim 1, in which the slurry is treated hydrothermally for about 15 min to about 6 hours.

9. The process of claim 1, in which the hydrothermal treatment is carried out in a tubular autoclave.

10. The process of claim 1, in which the slurry to be treated initially contains about l040 g of H SO /l of slurry.

11. The process of claim 4 in which the ferrite is zinc ferrite.

13. The process of claim 1, in which theslurry is 12. The process of claim 1, in which the slurry to be treated hydrothermally for about 15 minutes to about 3 treated has a solid material content of about 200-500 hours UNITED STATES PATENT OFFICE @E 'HHQAT 0F CCTION PATENT NO. 3910784 DATED October 7, 1975 INVENTOR(S) Jussi Rastas It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Col 7 Line 14. .before "process" the word "zone" should be zinc Col. 12 Line 51....after "about", "160 14 200 C" should be l60-2OO C Signd and ealcd this first Day 0? June1976 {semi Arrest.-

RUTH C. MASON Arresting Officer c. MARSHALL DANN Commissioner nfParems and Trademarks 

1. A process for the preparation of a raw material suitable for iron production from a precipitate derived from an electrolytic zinc process and comprising basic sulfates and hydroxides of iron and zinc ferrite, and for recovering other metal values in the precipitate, comprising: forming a slurry of the precipitate in water; converting iron in said slurry into haematite Fe2O3 by treating said slurry hydrothermally in an autoclave at a temperature between about 150*C and about 280*C while maintaining operating conditions within the stability range of haematite Fe2O3 in the system Fe2O3-SO3-H2O to form haematite containing solid material suitable for iron production and a solution containing said other metal values; and separating said haematite containing solid material from said solution.
 2. The process of claim 1, in which the precipitate is slurried in water mildly acidified with sulfuric acid.
 3. The process of claim 1, wherein the precipitate contains zinc ferrite and At least one of the following basic sulfates of iron: glockerite, ferrihydroxosulfate, and jarosite A/Fe3(SO4)2(OH)6/, in which A is selected from the group consisting of an alkali metal ion, NH4 and H3O .
 4. The process of claim 1, wherein the precipitate contains at least one of the following hydroxides of iron, namely goethite and a ferrite.
 5. The process of claim 1 for treating a precipitate containing mainly glockerite and zinc ferrite, in which the hydrothermal treatment is carried out at a temperature of about 160*14 200*C.
 6. The process of claim 1 for treating zinc ferrite and a pure jarosite precipitate, in which the hydrothermal treatment is carried out at a temperature of about 220*-250*C.
 7. The process of claim 1, in which the slurry to be treated has a solid material content of about 200-800 g/l.
 8. The process of claim 1, in which the slurry is treated hydrothermally for about 15 min to about 6 hours.
 9. The process of claim 1, in which the hydrothermal treatment is carried out in a tubular autoclave.
 10. The process of claim 1, in which the slurry to be treated initially contains about 10-40 g of H2SO4/l of slurry.
 11. The process of claim 4 in which the ferrite is zinc ferrite.
 12. THE PROCESS OF CLAIM 1, IN WHICH THE SLURRY TO BE TREATED HAS A SOLID MATERIAL CONTANT OF ABOUT 200-500 G/L.
 13. The process of claim 1, in which the slurry is treated hydrothermally for about 15 minutes to about 3 hours. 